1. Field of the Invention
This invention relates to a small watercraft and more particularly to the layout of engine components within the watercraft.
2. Description of Related Art
Personal watercrafts have become very popular in recent years. This type of watercraft is sporting in nature and carries one, two or three passengers. A relatively small hull of the personal watercraft commonly defines a rider""s area above an engine compartment. An internal combustion engine frequently powers a jet propulsion unit which propels the watercraft. The engine lies within the engine compartment in front of a tunnel formed on the underside of the watercraft hull. The jet propulsion unit is located within the tunnel and is driven by a driveshaft. The driveshaft usually extends between the engine and the jet propulsion device, through a wall of the hull tunnel.
The engine generally has an air induction system and an exhaust system both are completely dispersed onto the starboard and the port side. However, if the engine has a relatively large displacement and/or a plurality of combustion chambers for increasing its power output, the exhaust system must have a long exhaust conduit that surrounds the engine per se. In other words, the exhaust conduit extends to the space where the air induction system is located because the engine compartment is only allowed to have a limited space within the small watercraft.
For example, an exhaust manifold is connected to exhaust ports that open at a side wall of a cylinder block. An exhaust conduit extends from the exhaust manifold forwardly, then crosses the front and upper portion of the cylinder block and goes to rearwardly along the opposite side wall. After that, the exhaust conduit is turned from the upper position of the opposite side wall to the lower position slantwise at the rear portion of the cylinder block. Then, the exhaust conduit is finally connected, via a water lock, to a side wall of a jet pump compartment for opening thereto.
As is apparently understood, the capacity for the air induction system is restricted unless any measures are taken in this arrangement. The air induction system generally has an air chamber or silencer at its tip portion, which must have a relatively large volume for proper function. However, this volume will be reduced in the aforenoted arrangement. Unless the induction system has a sufficient volume, a necessary amount of air charge for combustion may not be supplied to the combustion chamber(s).
Also, if an outlet opening of the exhaust manifold opens upwardly, the exhaust conduit extends upwardly from the outlet opening of the exhaust manifold. However, because of the compact nature of the engine compartment again, the height of the exhaust conduit is restricted. Thus, it is necessary to bend the exhaust conduit with a relatively small curvature. This small curvature, however, is likely to hinder exhaust gasses from smooth flowing at the connecting portion of the exhaust manifold with the exhaust conduit. As a result, the attempt for increasing power output of the engine is greatly difficult.
Further, if the engine has multiple combustion chambers, usually it is equipped with a plurality of carburetors corresponding to the respective combustion chambers. The multiple carburetors are located at one side of the cylinder block so that each carburetor is positioned at each combustion chamber. As described above, some part of the exhaust conduit is also placed at this side of the cylinder block. Conventionally, all of control members for the carburetors are usually positioned at upper sides thereof Generally, the control members are throttle levers for operating respective throttle valve shafts, a rod for connecting the multiple throttle levers, a pulley connected to one of the throttle valves and a control wire wound around the pulley and connected to an accelerator positioned at a steering handle of the watercraft. In addition, an adjuster for adjusting idle openings of respective carburetors is also placed at the same upper side thereof so that a passenger or rider of the watercraft may easily access to them for the adjustment.
However, due to the abovedescribed arrangement of the exhaust system, the throttle levers are likely to be influenced by heat which the exhaust conduit may have during the engine operation. This causes thermal expansion in the control members of the carburetors because the members are made of metal. Accordingly, errors in movements of the control members can occur.
Also, in order to prevent the throttle levers and the pulleys from interfering with each other, either one of them should be somewhat remotely located from the carburetor bodies. This gives rise to need of large sized carburetors.
It is, therefore, a principal object of this invention to provide a compact engine that is most suitable to the small watercraft described above.
It is another object of this invention to provide an engine wherein an air chamber in an air induction system has the utmost volume even though an exhaust system is located in the proximity to the air chamber.
It is a further object of this invention to provide an engine that has an exhaust system through which exhaust gasses flow smoothly.
It is still a further object of this invention to provide an engine wherein throttle valve control members are disposed in compact nature on carburetors without producing any damages by heat from an exhaust system located in the proximity to the carburetors.
In addition, a cooling system for the engine of the small watercraft, specifically an engine block and an exhaust system, is arranged to be supplied with water, as a coolant, that is partially divided from the pressurized water generated by the jet propulsion unit in the hull tunnel.
The divided and pressurized coolant or cooling water is sent to a water jacket in the exhaust manifold with cooling water delivery pipes. The water goes to a water jacket in the engine body and then goes to a water jacket in the exhaust conduit. After that, it is delivered to the inside of the exhaust conduit per se upstream of the water lock so as to cool exhaust gasses therein and finally discharged to the outside of the watercraft.
Conventionally, each of the cooling water delivery pipes is made of rubber and connected independently to each inlet opening formed at respective branch portions of the exhaust manifold that correspond to respective cylinders or combustion chambers of the engine. However, the respective delivery pipes generally have different lengths from the jet propulsion unit. Because of this arrangement, it is difficult to deliver cooling water uniformly to respective cylinders and it is not an easy work to connect respective delivery pipes to the respective inlet openings of the exhaust manifold.
It is, therefore, still another object of this invention to provide an engine wherein cooling water can be uniformly delivered to respective cylinders and also the work for furnishing a delivery pipe is relatively easy.
Further, some carburetors have an acceleration pump mechanism to increase fuel supply when the rider desires to accelerate the watercraft. However, if air or bubbles exist in the acceleration pump mechanism and/or contiguous fuel supply pipes, performance of the carburetors for acceleration can be damaged.
It is, therefore, a further object of this invention to provide an engine wherein carburetors are allowed to discharge bubbles as soon as possible.
In accordance with a first aspect of this invention, an engine is adapted to be embodied in a watercraft having a hull and a propulsion device carried by the hull and driven by the engine for propelling the watercraft. The engine comprises an engine body having at least one combustion chamber. The engine also comprises an air induction system extending from the engine body for inducing air charge into the combustion chamber and an exhaust system extending from the engine body for discharging exhaust gasses from the combustion chamber. The air induction system includes an air chamber having a relatively large volume. The exhaust system includes a passage portion existing in the proximity to the engine body. At least a part of the air chamber of the air induction system is placed under the passage portion of the exhaust system.
In accordance with a second aspect of this invention, an engine is adapted to be embodied in a watercraft having a hull and a propulsion device carried by the hull and driven by the engine for propelling the watercraft. The engine comprises an engine body having a plurality of combustion chambers and an exhaust system for discharging exhaust gasses from the combustion chambers. The exhaust system includes an exhaust manifold extending from the engine body and having an opening end, and a contiguous conduit connected to the opening end of the exhaust manifold and extending generally along the engine body. The opening end of the exhaust manifold inclines toward the direction in which the contiguous conduit extends.
In accordance with a third aspect of this invention, an engine is adapted to be embodied in a watercraft having a hull and a propulsion device carried by the hull and driven by the engine for propelling the watercraft. The engine comprises an engine body having a plurality of combustion chambers, an exhaust system for discharging exhaust gasses from the combustion chambers and a cooling system for cooling the engine body and the exhaust system. The exhaust system includes an exhaust manifold extending from the engine body and having a plurality of branches corresponding to the combustion chambers. The cooling system includes a coolant jacket extending through the manifold. The coolant jacket has openings at each end of the branches. The engine further comprises a single coolant delivery conduit having delivery openings connected to the branch openings for delivering coolant.
In accordance with a fourth aspect of this invention, an engine is adapted to be embodied in a watercraft having a hull defining a rider""s area and a propulsion device carried by the hull and driven by the engine for propelling the watercraft. The engine comprises an engine body having a plurality of combustion chambers. The engine also comprises a plurality of carburetors corresponding to the combustion chambers and each having a throttle valve for supplying air fuel mixture for combustion in the each combustion chamber. The engine further comprises a control mechanism for controlling an opening of the throttle valve remotely from the rider""s area. The engine still further comprises an interlocking mechanism for activating the throttle valves synthetically. The control mechanism is positioned at one side of the carburetors and the interlocking mechanism is positioned at another side of the carburetors.
In accordance with a fifth aspect of this invention, an engine is adapted to be embodied in a watercraft having a hull and a propulsion device carried by the hull and driven by the engine for propelling the watercraft. The engine comprises an engine body having a plurality of combustion chambers and a plurality of carburetors corresponding to the combustion chambers having throttle valves for supplying air fuel mixture for combustion in the each combustion chamber. The engine further comprises a fuel increase mechanism placed at one carburetor located at the most rearward position relative to the watercraft and having fuel supply conduits for supplying fuel to the respective carburetors.
Further aspects, features and advantages of this invention will be become apparent from the detailed description of the preferred embodiments which follow.